The native heart valves (i.e., the aortic, pulmonary, tricuspid and mitral valves) serve critical functions in assuring the forward flow of an adequate supply of blood through the cardiovascular system. These heart valves can be rendered less effective by congenital malformations, inflammatory processes, infectious conditions, or disease. Such damage to the valves can result in serious cardiovascular compromise or death. For many years the definitive treatment for such disorders was the surgical repair or replacement of the valve during open heart surgery. However, such surgeries are highly invasive and are prone to many complications. Therefore, elderly and frail patients with defective heart valves often went untreated. More recently, transvascular techniques have been developed for introducing and implanting prosthetic devices in a manner that is much less invasive than open heart surgery. Such transvascular techniques have increased in popularity due to their high success rates.
A healthy heart has a generally conical shape that tapers to a lower apex. The heart is four-chambered and comprises the left atrium, right atrium, left ventricle, and right ventricle. The left and right sides of the heart are separated by a wall generally referred to as the septum. The native mitral valve of the human heart connects the left atrium to the left ventricle. The mitral valve has a very different anatomy than other native heart valves. The mitral valve includes an annulus portion, which is an annular portion of the native valve tissue surrounding the mitral valve orifice, and a pair of cusps or leaflets extending downward from the annulus into the left ventricle. The mitral valve annulus can form a “D” shaped, oval, or otherwise out-of-round cross-sectional shape having major and minor axes. The anterior leaflet can be larger than the posterior leaflet, forming a generally “C” shaped boundary between the abutting free edges of the leaflets when they are closed together.
When operating properly, the anterior leaflet and the posterior leaflet function together as a one-way valve to allow blood to flow only from the left atrium to the left ventricle. The left atrium receives oxygenated blood from the pulmonary veins. When the muscles of the left atrium contract and the left ventricle dilates (also referred to as “ventricular diastole” or “diastole”), the oxygenated blood that is collected in the left atrium flows into the left ventricle. When the muscles of the left atrium relax and the muscles of the left ventricle contract (also referred to as “ventricular systole” or “systole”), the increased blood pressure in the left ventricle urges the two leaflets together, thereby closing the one-way mitral valve so that blood cannot flow back to the left atrium and is instead expelled out of the left ventricle through the aortic valve. To prevent the two leaflets from prolapsing under pressure and folding back through the mitral annulus toward the left atrium, a plurality of fibrous cords called chordae tendineae tether the leaflets to papillary muscles in the left ventricle.
Mitral regurgitation occurs when the native mitral valve fails to close properly and blood flows into the left atrium from the left ventricle during the systolic phase of heart contraction. Mitral regurgitation is the most common form of valvular heart disease. Mitral regurgitation has different causes, such as leaflet prolapse, dysfunctional papillary muscles, and/or stretching of the mitral valve annulus resulting from dilation of the left ventricle. Mitral regurgitation at a central portion of the leaflets can be referred to as central jet mitral regurgitation, and mitral regurgitation nearer to one commissure (i.e., the location where the leaflets meet) of the leaflets can be referred to as eccentric jet mitral regurgitation.
In addition to mitral regurgitation, mitral narrowing or stenosis is most frequently the result of rheumatic disease. While this has been virtually eliminated in developed countries, it is still common where living standards are not as high.
Similar to complications of the mitral valve are complications of the aortic valve, which controls the flow of blood from the left ventricle into the aorta. For example, many older patients develop aortic valve stenosis.
One method for treating valvular heart disease includes the use of a prosthetic valve implanted within the native heart valve. These prosthetic valves can be implanted using a variety of techniques, including various transcatheter techniques, in which a prosthetic valve is mounted in a crimped or compressed state on the distal end portion of a delivery catheter. The delivery catheter is then advanced through the patient's vasculature until the prosthetic valve reaches the implantation site. The valve at the catheter tip is then expanded to its functional size at the site of the defective native valve such as by inflating a balloon on which the valve is mounted. Alternatively, a self-expanding prosthetic valve can be retained in a radially compressed state within a sheath of a delivery catheter. After the distal end of the delivery catheter is advanced to the implantation site, the prosthetic valve can be deployed from the sheath, which allows the prosthetic valve to expand to its functional state.
Although prosthetic valves for implantation at the aortic valve are well-developed, catheter-based prosthetic valves are not necessarily applicable to the mitral valve due to the distinct differences between the aortic and mitral valves. For example, the mitral valve has a complex subvalvular apparatus, i.e., chordae tendineae, which is not present in the aortic valve. Additionally, the native mitral valve annulus typically does not provide sufficient structure for anchoring and resisting migration of a prosthetic valve.
In recent years, significant efforts have been made in developing prosthetic valves for implantation at the native mitral valve. However, these prosthetic valves can require very difficult and accurate placement which, in turn, leads to unsuccessful or undesirable placement or long procedural times. These constraints can adversely affect a patient's health both during and after the implantation procedure or even prevent some patients from being able to undergo the procedure all together.
As such, there is a continuing need for improved prosthetic valves, as well as methods for implanting such prosthetic valves.